Automatic blood pressure monitors are commonly used to periodically measure the blood pressure of a patient. In most automatic blood pressure monitors, a pressure cuff is attached to a patient's arm over the brachial artery. The cuff is first pressurized with an applied pressure that is high enough to substantially occlude the brachial artery. The cuff pressure is then gradually reduced, either continuously or in increments. As the pressure is reduced to systolic pressure, the flow of blood through the brachial artery beneath the cuff increases substantially.
When the blood flows through the brachial artery following each contraction of the heart, it imparts a pulsatile movement to the wall of the artery. This pulsatile movement is coupled to a blood pressure cuff extending over the artery as minute changes in the cuff pressure, which are known as oscillometric pulses. Automatic blood pressure monitors measure and record the amplitude of the oscillometric pulses at a number of cuff pressures. After the blood pressure measurement had been completed, a table contains the oscillometric pulse amplitudes recorded at each cuff pressure.
In theory, the systolic, diastolic, and mean arterial blood pressures can then be determined from the values in the table using empirical definitions of these parameters as a function of the amplitudes of these oscillometric pulses. However, blood pressure measurements are often adversely affected by artifact, generally produced by patient movement. Motion-induced artifacts can substantially alter the measured amplitude of oscillometric pulses thus introducing inaccuracies in the measurement of the patient's blood pressure.
Prior systems use various techniques to minimize the effects of artifacts. Some prior systems screen oscillometric pulses based on their amplitude. Pulses with amplitudes outside the screen are considered artifact-induced. The screen is generally a population-based screen and not specific to any patient. Some previous systems also compare sequential pulses to ensure they are blood pressure induced. If two sequential pulses have similar amplitudes, these systems assume the pulse is blood pressure induced. However, these screening and comparison techniques do not always produce acceptable results. It would be desirable to have a system in which the screening and comparing of pulses more accurately identifies blood pressure induced pulses.